1. Field of the Invention
The present invention relates to ground fault circuit interrupters (GFCI), and in particular, to interrupters having a latch means for holding a pair of movable contacts against a pair of stationary contacts.
2. Description of Related Art
A ground fault occurs when current improperly flows through a ground line. Such a current flow indicates that an improper current path has been made from the primary power lines. Such a condition may indicate a shock hazard, even when the current flow is insufficient to trip the main breaker. Known ground fault circuit interrupters have been mounted in a receptacle housing with a detector to sense the ground fault condition. A ground fault is often detected by determining whether there is an imbalance in current between the two primary power lines. One or more toroidal coils can encircle the primary power lines to detect an imbalance in the currents in those lines. The imbalance can produce an output voltage from the toroidal coil to trigger a semiconductor circuit that energizes a solenoid coil. The solenoid coil can drive an armature to release a latch that otherwise holds a pair of moveable contacts against a pair of stationary contacts. When the moveable contacts are released, power is disconnected from the sockets on the receptacle protected by the ground fault circuit interrupter.
A known GFCI has in its bottom compartment an L-shaped, spring-loaded latch that is slidably mounted in grooves in the base of a rectangular block having an axial bore. Two arms extend from the rectangular block for deflecting a pair of cantilevered, moveable contacts. A spring-biased reset button is molded onto a metal pin having an annular groove adjacent a tapered tip. This pin is designed to extend through the axial bore in the rectangular block and engage a central hole in the L-shaped, sliding latch. The tapered tip pushes through this hole to retract the sliding latch. When the annular groove on the pin reaches the hole in the spring-loaded latch, it latches onto the groove on the pin. Thereafter springs on the reset button lift the pin and the rectangular block to drive the cantilevered contacts against stationary contacts, in order to power the outlet sockets of the GFCI.
A solenoid is mounted adjacent to this sliding, L-shaped latch. When actuated, the solenoid armature is pulled into the solenoid coil to compress a solenoid spring and slide the spring-loaded latch to an unlatched position, thereby releasing the pin of the reset button. This allows the rectangular block and the latch to disengage the cantilevered contacts, which now return to their neutral position, spaced from the fixed contacts.
Another GFCI of this type is shown in U.S. Pat. Nos. 5,510,760 and 5,594,398. In these references, the latch is in the form of a single metal stamping, shaped to include an integral spring. This latch is not mounted to slide in grooves on a latch block, but is simply mounted below a latch block used to lift moveable contacts. The latch is operated when the armature of a solenoid extends to push the latch and release a latch pin, which then lifts the latch block to close the contacts. A disadvantage with this device is the tendency of the latch to become magnetized and stick to the armature. Also, the armature must receive a relatively high electromotive force before overcoming friction with the latch pin.
The GFCI in U.S. Pat. No 4,630,015 has a solenoid armature that pushes cam actuators to separate contacts and thereby remove power from outlet sockets. See also U.S. Pat. No. 5,223,810.
The GFCI shown in U.S. Pat. No. 4,802,052 has an L-shaped latch plate that is pulled, not pushed, by a solenoid armature. For this reason, the latch has a pair of legs that straddle the solenoid armature between a spaced pair of collars. The GFCI in U.S. Pat. No. 4,595,894 also has a latch plate with a pair of legs that straddle a groove on a solenoid armature. When this solenoid retracts, it pulls the latch plate to release a pair of moveable contacts.
Also, the solenoid coil in U.S. Pat. No. 4,595,894 is mounted above a separator inside a receptacle housing. The solenoid coil is near the longitudinal center of the housing. The latch plate that connects to the tip of the solenoid armature is directed to extend back under the solenoid coil. This requires a great deal of the latching mechanism to be placed in a crowded area that contains the solenoid coil and other mechanisms.
A typical disadvantage with the foregoing GFCI units is that the solenoid coil is crowded, often against the latch mechanism or the ground fault detecting circuitry. To accommodate the solenoid and to allow room for the latching mechanism, these solenoid coils are generally mounted to one end of the compartment. While the solenoid coil in U.S. Pat. No. 4,595,894 is centrally mounted in a different compartment than the ground fault detecting circuit, its latching mechanism tends to be crowded around the solenoid coil.
Other GFCI units are shown in U.S. Pat. Nos. 5,260,676; 5,457,444; 5,477,201; and 5,517,165. See also U.S. Pat. Nos. 5,264,811; and 5,563,756.
A significant disadvantage with the foregoing latch mechanisms is the relatively high resistance to initially moving the latch. A latch plate must typically overcome friction to slide past a shoulder or other engagement surface before being released. Once the latch plate moves the rather small distance needed for release, the latch plate can then slide with very little resistance, other than spring biasing.
Accordingly, the bulk of the useful energy consumed by the solenoid coil is only for the initial period when the frictional resistance must be overcome. Consequently, the solenoid coil will need a relatively high current while the armature is stalled to produce enough magneto motive force to eventually move the armature. Therefore, solenoid coils are usually over designed, simply to provide sufficient initial force required to overcome the friction.
Accordingly, there is a need for an improved GFCI that uses space efficiently and has a solenoid that is adapted to efficiently overcome the frictional forces associated with releasing a latch mechanism.